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Primary Science · Year 5Chapter 6 · Solutions and separating mixtures
Year 5 Science · Solutions and separating mixtures · Lesson 6.3

Year 5 Science: Recovering a solid from a solution

Part of the Year 5 Science solutions and separating mixtures chapter. Chapter overview · whole chapter on one page

6.3

Recovering a solid from a solution

Year 5
M3: describe how to recover a substance from a solution, by evaporating the water
Story. Ruby has a dish of salt water that has been left on a sunny windowsill for several days. “The water has gone, and there is white salt in the dish,” she says. “How did the salt come back?”

The salt can be recovered from the solution by evaporation. The water in the dish turns into water vapour, and it goes into the air. The salt does not evaporate, so it is left behind in the dish as crystals.

Evaporation happens faster in a warm, dry place, and on a dish with a large surface. It is safest to leave the dish somewhere warm and dry, rather than heating it.

water evaporates; salt is left in the dishwater vapour in the air
A dish of salt water. The water evaporates into the air, and salt crystals are left in the dish.

The table shows the mass of salt left in a dish, from a fair test. The dish was kept in the same warm, dry place each day.

Days in a warm, dry placeGrams of salt left in the dish
00
14
28

Key ideas

  • Evaporation turns the water in a solution into water vapour.
  • The dissolved solid does not evaporate, so it is left behind as crystals.
  • Evaporation is faster in a warm, dry place, and on a wide dish.
  • Recovering a solid from a solution is done by evaporating the solvent.
Worked example 6.3.1
Which substance is left in the dish when the water has evaporated? Write the word.

Method. Think about what evaporates.

  1. Think about the water. The water turns into vapour and goes into the air.
    water vapour
  2. Name the substance left. The salt does not evaporate, so the salt is left in the dish.
    salt
  3. Write the answer.
    salt

Check. The salt crystals are the recovered solid. ✓

Worked example 6.3.2
Look at the salt table in section 6.3. How many grams of salt were left after 2 days? Write the number.

Method. Find the row for 2 days.

  1. Find the row. The row for 2 days shows 8 grams of salt.
    2 days
  2. Read the mass. The mass of salt left after 2 days is 8 grams.
    8
  3. Write the answer.
    8

Check. The mass grows as the water leaves. ✓

Worked example 6.3.3
Why is it safer to leave the dish of salt water somewhere warm and dry, rather than heating it? Write one word for the reason: safe or fast.

Method. Think about why the dish is left out.

  1. Think about heating. Heating a dish needs a flame or a hot surface, which can be dangerous.
    dangerous
  2. Choose the word. Leaving it in a warm place is safer, so the reason is safe.
    safe
  3. Write the answer.
    safe

Check. Accept any answer that says it is safer. ✓

Watch out

Watch out: evaporation takes the water out of the solution, not the solid. The salt is still there, as crystals in the dish.

Try it (with your teacher). With your teacher, put one teaspoon of salt into a small dish of warm water and stir it until it dissolves. Leave the dish on a sunny windowsill or in a warm place for two or three days. Look at it each day and write what you see. Do not taste the salt or the water.

Exam tip

Grown-up tip. Ask: “Where has the water gone? Why is the salt still there?” Let your child predict what will happen, then check each day.

Exercise 6C  Recovering a solid from a solution

1
FWhat is the name for the process in which the water in a solution turns into a gas, and goes into the air? Write the word.
2
FAfter the water has evaporated from salt water, what is left in the dish? Write the word.
3
FLook at the salt table in section 6.3. How many grams of salt were left after 1 day? Write the number.
4
FLook at the salt table in section 6.3. How much more salt was left after 2 days than after 1 day? Write the number of grams.
5
PSLook at the salt table in section 6.3. At which day was there no salt left in the dish? Write the number of days.
6
FFill in the gap: evaporation takes the ___ out of the solution. Write one word.
7
FFill in the gap: the dissolved solid is recovered by ___. Write one word.
8
PSIs evaporation faster in a warm place or a cold place? Write the word: warm or cold.
9
PSAli says: “The salt evaporated along with the water.” Is Ali right? Write yes or no.
10
PSWorking scientifically. Predict the result. Predict what will be left in the dish if a sugar and water solution is left in a warm place. Write the word.
11
RExplain why the salt is still in the dish after the water has evaporated. Write one sentence.

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